ST. PETERSBURG — They moved rocks and steel beams Saturday with their hands and heavy machinery, laboring gingerly over the massive, unsteady pile. They searched for signs of life with seismic listening devices, telescoping cameras and search-and-rescue dogs.

But for a second day, there was no sign of the missing welder, Clark White.

So at 5 p.m. Saturday, the rescuers searching for White, 65, altered their objective. When they resume their task today, their aim will be to recover the missing man's body.

"All of those things have failed. They have been unsuccessful," said Alan Rosetti, the St. Petersburg Fire Rescue division chief who led the rescue effort Saturday.

The decision was not an easy one, Rosetti said.

White's family, which flew in from West Virginia to be close to the Progress Energy plant on Weedon Island, was there as crews worked from daylight to late afternoon. Relatives were told of the search team's decision, Rosetti said.

He said the rescue team will resume the recovery effort at daybreak Sunday, and not stop until it finds White's body.

The search team, 25 specially trained firefighters from Hillsborough and Pinellas counties, had moved 50 to 60 feet of debris to isolate an area 20 feet wide by 28 feet long. Rescuers hoped White had found safety in a void — a small empty cave created by fallen debris. But those expectations dimmed Saturday, Rosetti said, as rescuers realized that there were fewer voids than expected.

"Whatever we do is in the best interests of the personnel who have been working here," Rosetti said.

White, a father, grandfather and Army veteran, was on the ground floor when he was last seen running away from the falling structure. Before the collapse, he was wielding a torch to cut structural beams. The building, an old oil-fired plant that was decommissioned two years ago, was supposed to come down at 8:30 p.m. after workers strapped cables to supports and used heavy machinery to pull on them, Progress Energy said.

But something went wrong. White became trapped as the 180-foot-tall building prematurely collapsed.

White, a veteran in the demolition industry, warned other crew members — including his son, Travis, 31 — just before the power plant came down, his family told the St. Petersburg Times. He works for Frontier Industrial Corp. of Buffalo, N.Y., which was hired to demolish the building.

White has more than 15 years of experience and worked as an industrial dismantling specialist, according to the company.

Federal investigators have been on the site for days, but an investigation into what went wrong will not begin until the recovery is over, Progress Energy officials said.

The collapsed building was one of three that housed boilers used to generate electricity at the plant, which opened in 1958. In operation since 1963, the fallen building was the last of the three steam units added to the site.

Progress Energy took all three units offline in 2009 when new natural gas-powered plants went into service at the plant.